Microsoft 365 Business Premium vs E3: Which License Fits a Regulated Firm

What's the difference between Business Premium and E3?

Business Premium is Microsoft’s security bundle for small and mid-sized firms, and it stops at 300 users. Microsoft 365 E3 is the enterprise plan, and it has no cap. Under 300 seats, Business Premium actually includes more email security than E3. E3’s edge is room to grow and Windows 11 Enterprise.

Microsoft describes Microsoft 365 for enterprise as “designed for large organizations” that can also be used by smaller firms “that need the most advanced security and productivity capabilities.” Its components are the Microsoft 365 Apps, Windows 11 Enterprise, Intune, and Defender for Endpoint. E5 includes all of E3 plus the Defender Suite and Purview Suite.

Business Premium is described as “designed especially for small and medium-sized businesses (up to 300 users)” on Microsoft’s Business Premium overview. For a regulated firm of 5 to 100 people, that’s the plan we start from.

If you’re still choosing a platform and not a plan, start with our Google Workspace vs Microsoft 365 guide.

What is the 300-user limit on Business plans?

The limit is 300 seats total across all Business plans in one tenant, not 300 per plan. Microsoft’s Business Premium FAQ says organizations “may only provision up to 300 seats total across all of our Business family of plans (Business Basic, Business Standard, Business Premium).”

Microsoft’s own example: if you have 250 seats of Business Premium, you can add only 50 more seats across all Business plans. Microsoft “reserves the right to enforce the tenant limit,” and it tells organizations with more than 300 users to look at the enterprise plans.

The cap counts provisioned seats, not just Premium seats. A part-time assistant on Business Basic still uses one of the 300. If you’re at 220 and hiring, plan the move to E3 before you hit the wall, not the week you do.

What security features does Business Premium include?

Business Premium is Business Standard plus the security stack. Microsoft’s business security overview and the Business Premium security FAQ list what you get:

• Microsoft Entra ID P1. This is what unlocks Conditional Access: rules like “require MFA everywhere,” “block legacy sign-ins,” or “only allow compliant devices to open email.” The Conditional Access overview confirms Business Premium customers can use it.
• Microsoft Intune Plan 1. Full device and app management for Windows, Mac, iOS, and Android, including app protection for personal phones.
• Microsoft Defender for Business. Endpoint protection that Microsoft calls equivalent to Defender for Endpoint Plan 1 with some Plan 2 features, including endpoint detection and response.
• Microsoft Defender for Office 365 Plan 1. Safe Links, Safe Attachments (including for SharePoint, OneDrive, and Teams), and impersonation protection in anti-phishing policies.
• Microsoft Purview. Per Microsoft’s Purview service description, Business Premium covers manual sensitivity labels, Message Encryption, DLP for Exchange, SharePoint, and OneDrive, retention policies and labels, and an archive mailbox up to 1.5 TB.

For a CPA firm, a title agency, or a medical practice, that list covers the controls an auditor or cyber insurer asks about: MFA, managed devices, endpoint detection, encryption, and email protection.

What does E3 have that Business Premium doesn't?

E3’s main advantage is scale. There’s no 300-seat ceiling. It also includes Windows 11 Enterprise, and Microsoft sells the Defender Suite and Purview Suite as add-ons on top of E3.

On security, E3 and Business Premium overlap more than they differ. Both include Entra ID P1, Intune, manual sensitivity labels, Message Encryption, and DLP for email and files. One gap runs the other direction. Microsoft’s Defender service description lists Business Premium and E5 for Defender for Office 365 Plan 1, and E3 isn’t on that list. E3 includes Defender for Endpoint Plan 1 for devices, but no Safe Links or Safe Attachments unless you add them.

For a firm that loses money through its inbox, that matters. A 150-person firm moving from Business Premium to E3 for “more security” can actually lose email protection.

When does E3 or E5 make sense?

Move to E3 when you pass 300 users or you’re about to. Look at E5 when your regulator, your insurer, or your own risk calls for features Business Premium doesn’t have:

• Risk-based Conditional Access. Sign-in risk and user risk policies need Microsoft Entra ID Protection, a P2 feature. Microsoft’s Entra licensing page lists P2 in E5, not in E3 or Business Premium. P2 also unlocks Privileged Identity Management for time-limited admin roles.
• Premium eDiscovery and Audit. E3 covers eDiscovery (Standard) and Audit (Standard). Premium eDiscovery and Audit (Premium) come with E5.
• Insider Risk Management, Customer Lockbox, Endpoint DLP, and automatic sensitivity labeling. All E5-level in the Purview service description.

There’s a middle path under 300 seats. Microsoft sells a Defender Suite add-on and Purview Suite add-ons for Business Premium. The Defender Suite adds Entra ID P2, Defender for Endpoint Plan 2, Defender for Office 365 Plan 2, Defender for Identity, and Defender for Cloud Apps. The Purview add-ons, per Microsoft, “require a Microsoft 365 Business Premium base license and are capped at 300 seats total.”

Does buying Business Premium make you secure?

No. A license is permission to use a feature, not the feature working. Microsoft says so itself. After setup, “you need to review and configure the security settings,” per the business security overview.

Some protection is on by default. New tenants get security defaults, which require MFA registration and block legacy authentication. But Microsoft also says organizations with Entra ID P1 “security defaults are probably not right for you.” To use Conditional Access, you have to turn security defaults off, and Microsoft says to “immediately enable Conditional Access policies” after that. If someone flips the switch and never builds the policies, the tenant ends up with less protection than security defaults gave it.

The same goes everywhere else. Intune does nothing until devices are enrolled and compliance policies exist. Defender for Office 365’s defaults are a start, but Microsoft recommends turning on the Standard or Strict preset policies. Sensitivity labels don’t exist until someone creates them.

We’ve seen what “enrolled but not enforced” costs. In our business email compromise guide, the first fix is enforcing MFA at the tenant level on every Microsoft 365 or Google Workspace tenant you inherit. And MFA alone may not be enough. Our phishing-resistant MFA guide covers why. Intune and Entra also matter when a laptop won’t boot: we wrote up how to find a BitLocker recovery key that was escrowed to Entra ID.

Key takeaways

What this looks like when we do it

Most tenants we take over were set up years ago and never touched again: default settings, no Conditional Access, and licenses nobody has audited. Whatever plan you’re paying for, our Microsoft 365 administration work starts with identity. That means Conditional Access policies that enforce MFA, with security defaults turned off only after those policies are live. Then we harden email with mail-flow rules that stop silent forwarding, and we watch for odd sign-ins.

License management is part of the same job. We check who has what, who left and still holds a seat, and whether you’re headed for the 300-seat cap. If E3 or an add-on is the right call, we’ll tell you why. If it isn’t, we’ll tell you that too. More on how we run tenants is on our cloud solutions page.

Not sure which license you need, or whether the one you have is set up? Book a call and we’ll look at your tenant with you.